MD or DM? Modified dynamics at low accelerations vs dark matter

Abstract

The MOND paradigm posits a departure from standard Newtonian dynamics, and from General Relativity, in the limit of small accelerations. The resulting modified dynamics aim to account for the mass discrepancies in the universe without non-baryonic dark matter. I briefly review this paradigm with its basic tenets, and its underlying theories--nonrelativistic and relativistic--including a novel, bimetric MOND gravity theory. I also comment on MOND's possible connection to, and origin in, the cosmological state of the universe at large. Some of its main predictions, achievements, and remaining desiderata are listed. I then succinctly pit MOND against the competing paradigm of standard dynamics with cold, dark matter. (Abridged)